"Drinking water entering New York Citys distribution system is treated with chlorine, fluoride, food grade phosphoric acid and, in some cases, sodium hydroxide. New York City uses chlorine to meet the New York State Sanitary Code SDWA disinfection requirements. Fluoride, added since 1966, at a concentration of one part per million, in accordance with the New York City Health Code, helps prevent tooth decay. Phosphoric acid is added to create a protective film on pipes that reduces the release of metals such as lead from household plumbing. Sodium hydroxide is added to Catskill/Delaware water to raise the pH and reduce corrosivity."